1. Field of the Invention
The present invention relates to a molding method and apparatus, and more particularly to an improved molding method and apparatus for investment-type molding of close-tolerance plastic articles, such as a dental prosthesis.
2. Description of the Related Art
Typically, a dental prosthesis, such as a full or partial denture, is prepared by forming the tooth-supporting and gum-contacting portion of the prosthesis in a closed mold cavity into which a plastic, denture base material is introduced. The replacement teeth are first properly positioned within the mold cavity, which is defined by two mold-cavity-defining mold portions, to assume the proper relative positions to replace the lost natural teeth when the prosthesis has been formed and is positioned within the mouth of the patient. The cavity-defining mold portions are separated and the material, which is often of a dough-like consistency, is positioned within the mold cavity. The mold portions are then pressed together, to compress the dough-like plastic material so that it flows to fill the mold cavity to unite with the teeth. The material is cured to form the desired prosthesis upon hardening of the plastic material.
Initially, a dentist takes an impression of the portion of the patient's mouth at which the prosthesis is intended to be positioned. The impression is in the form of a casting of plaster of paris, or other impression-defining material. When the impression material is removed from the patient's mouth and has become solidified it is packed with dental stone, which upon hardening conforms almost exactly in shape with that portion of the patient's mouth at which the finished prosthesis is to be positioned. The plaster of paris, or other impression material, is then separated from the dental stone impression.
The teeth that are to be a part of the finished prosthesis are then positioned in the appropriate place or places on the dental stone impression of the patient's mouth. The resulting stone impression and teeth are a duplicate of the patient's mouth, with replacement teeth in position. The stone impression accurately defines the surfaces of the patient's mouth and gums over which the prosthesis fits and on which it is supported when in use.
After the stone impression of the portion of the patient's mouth has been formed, a wax material is then applied to the surface of the stone impression in the desired thickness to define the thickness and outer shape of the finished prosthesis. The replacement teeth are then positioned on the wax pattern in the same position and in the same orientation that they would assume when part of the finished prosthesis. The stone impression and wax pattern are then placed in a suitable mold, and a complementary mold portion is provided by investment casting of plaster of paris over the surface of the prosthesis. Upon hardening of the plaster defining the complementary mold portion, the mold portion is separated from the impression material and the wax is removed by melting it and letting it flow from the respective mold portions. The result is a two-part mold that includes in one part the teeth to be incorporated into the prosthesis. The resulting mold cavity corresponds in shape and thickness with the shape and thickness of the final prosthesis.
Molding material is then placed between the two mold portions, which are then pressed together and held in a clamping fixture while the prosthetic material is undergoing a curing operation, such as by the application of heat. After curing the prosthesis is separated from the plaster mold portions, and is then trimmed, ground, and polished for ultimate use.
The prior art process hereinabove described most often utilizes a heat curable resin having the consistency of a dough. The dough is manually packed into the space between the upper and lower portions of the mold, and normally several trial packings are needed before the mold is finally properly packed and suitable for undergoing the curing operation. Such trial packings result in wasted molding material, and they involve repetitious and time consuming procedures.
It is an object of the present invention to eliminate the trial packing steps, with their consequent waste of material and waste of time.
It is another object of the present invention to provide a mold structure within which both investment material and the prosthesis material can be introduced to substantially eliminate processing errors.
It is a further object of the present invention to provide a mold member that is of light weight, and that is transparent to heat and microwaves for permitting curing of the molding material.